It is known that machines for preparing espresso coffee, typically used in bars and restaurants, require a dose of roasted and ground coffee to be placed in an extraction chamber provided with a filtering container. This container may be part of the so-called filter basket holder, which is filled by hand with the dose of ground coffee (typically 7±1 g for each cup to be dispensed) and subsequently mounted on the machine in order to proceed with the extraction of the beverage.
Machines for preparing espresso coffee are provided internally with a boiler for heating the water drawn from a tank or other source and a pump for sending to the delivery duct hot water at a selected pressure.
The traditional method for extracting the beverage by means of known machines consists typically of a first preinfusion step, in which the flow-rate of water entering at 90±2° C. is reduced for a certain time interval; a second impregnation step; and a third extraction step, in which the coffee cake is crossed by a stream of hot water at 90±2° C. at a constant pressure of 9 bars at the input of the cake of powdered coffee.
The beverage obtained from traditional espresso coffee machines is usually clearly distinguishable from the beverage obtained at home with coffee pots or infusion devices not only because the properties of flavor, aroma and body are different but also because the beverage obtained from traditional espresso coffee machines is characterized by a surface layer of foam, also known as crema. Crema is an attribute of the coffee beverage which is particularly appreciated by the consumer and is an indicator of correct preparation of the beverage.
As disclosed in WO 2005/092160 and WO 2005/092162, the Applicant of the present patent application has designed a particular capsule which contains a substance in powder form, preferably roasted and ground coffee, the capsule being provided with an elastic septum which generates crema and by means of which it is possible to extract a beverage with improved physical and organoleptic characteristics.
The known elastic septum is fixed downstream of the dose of substance in powder form and of the corresponding filter sheet and is characterized by an elastic membrane which has at least one through orifice or gap provided in a central region, so as to open and allow the passage of the beverage only when the internal pressure exceeds a certain value.
A drawback observed in known capsules is linked to the length of the capsule manufacturing time. In the particular case of capsules provided with an elastic septum, some operations which slow down the manufacturing process are linked to the preparation, installation and fixing of the elastic septum within the capsule.
Another drawback is due to the fact that typically capsules which contain ground coffee use paper-based filters in order to retain the solid fractions within the capsule and prevent them from being poured into the cup. The choice of paper-based filters can entail limitations in the design of the capsule; for example, it forces to design the bottom of the capsule so that there are no regions in which the filter paper might break due to the pressure inside the capsule or due to surface unevenness or openings.